Fiber application machines, commonly known as fiber placement machines, are known in particular through the document EP 0 626 252, in respect of the application to a mold of a strip formed of a number of fibers pre-impregnated with resin, the application roller coming into contact against the mold in order to apply the strip. The machine includes a gantry whereon an application head is mounted in order to allow it to move along a number of axes. Bobbins of pre-impregnated fibers are mounted on a creel joined to the robot, and conveyed from this creel to the application roller of the application head by specific conveying and guiding systems. Because of the adhesive aspect of resins, these conveying and guiding systems are particularly complex in design and tend to get clogged.
In order to guarantee that the pre-impregnated fibers unwind properly, and that the fiber width is substantially constant, the fibers are wound onto the bobbin with a separating film. The pre-impregnated fibers have a limited lifespan at ambient temperature and must be stored at temperatures of the order of −15° C. The placement machine must incorporate separating film removal systems which must guarantee a total and reliable removal of the separating film so as to prevent any risk of the manufactured part being polluted.
Current placement machines are proving to be particularly cumbersome and expensive. The different elements built onto the different displacement axes of the gantry or in the placement head, such as the bobbin creel, the conveying and guiding, cooling, and film removal systems, are cumbersome and heavy, and restrict the speed at which the fibers are applied. The machines do not allow fibers to be placed in parts of small dimensions or on some female molds because of the space requirement and the limited runs of the different axes.
Pre-impregnated fibers may have non-optimum mechanical characteristics, since the filaments constituting the fiber may be cut or discontinuous when the fiber comes from a pre-impregnated one-way slit strip, commonly known as “slit tape”.
The pre-impregnated fibers deposited on the molds must be subject to intermediate compaction operations so as gradually to discharge the air trapped between the folds in the deposited fibers. These compaction operations are performed either by installing a vacuum cover, or by continuous pressure of the fiber placement head on the mold, or by a combination of both methods. In both cases, the lead times are extended and the machine has to be designed so that it can exert this pressure.
To make the composite part, the pre-impregnated fibers are subjected to a polymerization operation in a vacuum or in an autoclave. To guarantee low porosity in the final composite it is necessary to effect a polymerization in autoclave, which considerably increases the implementation costs.
In the case of fibers stored on a bobbin, the built-in creels include a motor-driven unwinding system associated with each bobbin. Each unwinding system is automatically controlled as a function of the fiber speed so as to limit its tension at the application roller in order to guarantee in particular that it is placed flat on the concave surfaces of the molds. Each unwinding system is also automatically controlled as a function of robot displacement so that in particular slack can be recovered by re-winding the fiber. Such unwinding systems take up significant amounts of space and are very expensive and significantly restrict the bobbin unwinding speed on account of the automatic control constraints, and therefore the speeds at which the fibers are deposited.